Reliable, hygienic storage of items, such as food, is a major problem. For example, the problem is present throughout the food industry, e.g., manufacturers, retailers, restaurants, and in every household, and is especially significant for food service establishments, in which related issues of food quality control are also significant. In addition to food storage and quality control in fixed locations (e.g., a refrigerator) where access to electricity is readily available, proper food storage and quality control is also important in situations, such as picnics, camping, mobile food kiosks, hospitality or battlefield meal locations, search and rescue, etc., for which access to unlimited electricity and/or a stationary storage device, such as a refrigerator, is not available. In addition to food storage, other items also require hygienic storage. For example, medical and chemical equipment, construction wood, etc., also require storage in a biologically safe environment. Since ambient temperature significantly affects bacterial activity, effective control of the ambient temperature is an important tool in ensuring reliable, hygienic storage of various items.
In the food industry, bacteria, including those responsible for food-borne illness, often cannot be readily seen. Bacteria responsible for food-borne illness, such as Campylobacter jejuni, Clostridium botulinum, Clostridium perfringens, Escherichia coli O157:H7, Salmonella, Streptococcus A, Listeria monocytogenes, Shigella, Staphylococcus aureus, etc., can be present in food at the time of purchase or seeded during storage, particularly when packaging is opened or damaged. Such bacteria can be especially dangerous if present on food that is consumed without sufficient thermal treatment to kill the bacteria. Too often, humans and other animals suffer illness from the effects of undetected bacteria in food that was consumed. Other bacteria, which does not cause health problems, can affect the quality and taste of the food when present.
It has long been shown that ultraviolet radiation interacts with biologically active media. In particular, an absorption spectrum of a DNA molecule has a peak wavelength at about 265 nanometers, which is within the ultraviolet-C electromagnetic spectrum range of 100 to 280 nanometers. RNA and proteins also have absorption peaks in the ultraviolet-C electromagnetic spectrum range, from 215 to 280 nm. Therefore, the absorption of electromagnetic radiation within the UV-C range, and especially near 265 nanometers, as well as the photoluminescence in response to such radiation, is typically an indicator of biological activity, such as bacterial activity. Additionally, the more ultraviolet radiation that is absorbed by bacteria DNA, the more DNA molecules are destroyed, thereby preventing the reproduction process. As a result, ultraviolet radiation can be used to control bacterial growth.
However, detection of the presence of bacteria is often not sufficient to make a decision regarding spoilage or a condition of a stored item, such as food or a chemical. In particular, an intensity of a response to ultraviolet radiation strongly depends on the particular bacteria type(s), concentration(s), and location(s). Additionally, a similar fluorescent signal can be generated by certain food species, thereby providing a false indication of the presence of bacteria.